SURFACE COATING PROCESS

Abstract: A continuous process for surface coating of metal substrates on a coil coating line is described wherein as a first layer a paint material with adhesive properties is applied and dried and directly upon the hot paint surface of the first layer a clear, chlorine-free plastic sheet or foil is applied and cooled and on the cool plastic sheet or foil a pigmented, chlorine-free paint is applied and cured.

Description: SURFACE COATING PROCESS The present invention relates to a continuous process for surface-coating of metal substrates with planar surfaces, such as coil or sheet materials, on a coil-coating line for provid¬ ing a durable and corrosion protecting coating on the metal surface. The first layer is a paint material with adhesive properties. Examples of such suitable paint materials are polyester, vinyl or latex paints. After this first paint layer has been applied and dried a clear chlorine-free plastic sheet or foil of acrylic plastic, polyester or a similar polymer is applied directly upon the hot paint surface and then cooled. As/a third layer on the cooled plastic sheet or foil a pig en- ted, chlorine-free wet paint, such as latex, polyester, fluo- rocarbon polymers, e.g. P F2, or polyurethane (PUR) is app¬ lied. Said wet paint is cured (dried) and cooled after appli¬ cation. The paints are applied according to conventional techniques, such as roller coating, spray coating, curtain coating, etc. The drying is also performed by conventional methods, such as IR-tubes, induction or convection heating. After the first paint layer has been dried to a state of a certain degree of thermoplasticity the chlorine-free plastic sheet or foil is applied directly upon the hot paint surface. The plastic sheet is applied directly upon the hot paint surface by lamination, e.g. using a pressure roller. By means of the process according to the present invention a three layered surface coating is obtained which provides a very good corrosion protection to the metal substrate. The second layer, the chlorine-free plastic sheet or foil, has a thickness of from 10 to 300 μm. The third layer, the pigmented, chlorine-free paint, is app¬ lied to a thickness of from 10 to 150 μm dry film, preferably from 10 to 50 μm. It is previously known to treat metal sheeting, e.g. coming from a coil, by painting with a/primer layer and by applying a top coat on top of the primer layer. However, only a limited degree of corrosion resistance of the so-coated metal sheet is thereby obtained owing to a certain porosity in the coating layer materials. It is also previousJy known to treat the surface of e.g. metal sheet by first applying an adhesive layer and then applying a plastic sheet. Even in this case, a limited corrosion resis¬ tance is obtained owing to the fact that the adhesive layer is so thin. Furthermore, it is previously known from EP 0 233 179 to use PVC-plastisols as layers on metal sheet and also PVC-foils as the uppermost layer. However, this gives rise to pollution problems when chlorinated materials are broken down either in service or when recycled, and also gives rise to an impaired bonding of the total coating to the underlaying metal sub¬ strate over time owing to migration of plasticizers such aε phthalates to the interface between the metal substrate and the coating. SUBSTITUTE SHEET As metal materials with generally planar surfaces which can be treated with the surface coating process according to the present invention the following may be mentioned: cold rolled steel, metallized steel, stainless steel, galvanized steel, aluminium, etc. In the coating of sheet metal materials, the sheet metal is preferably pretreated chemically by usual methods, such as pickling, phos ' phatizing, chromating, etc. The invention is illustrated by means of the following Examples: Example 1 In a conventional coil coating line the following is applied on 0.8 mm hot galvanized steel, chemically pretreated with Bonder 1303 (a phosphatizing agent from Metallgesellschaft GmbH, Germany). First layer: A water borne acrylic paint (68760-34, Coilon laqua from Becker IndustrifSrg, Sweden) is applied by reverse -roller coat to a thickness of 10-25 μm dry film, drying/curing at 180°C PMT (peak metal temperature). Second layer: Directly upon the previous hot layer a clear thermoplastic acrylic sheet (Korad from Polymer Extruded Produσts Inc., USA) and a thickness of 75 μm is applied by laminating roller and a pressure of 3.5 kp/cm . Third layer: After the second layer has been cooled an acrylic water borne top coat (EJ 644-9302, Coilon Acrylic latex from Becker Industrifarg AB, Sweden) is applied to a thickness of 20 μm dry film, by reverse roller coat, drying/curing at 180°C PMT. SUBSTJTUTESHEET Example 2 The same aε Example 1 with the following exception: Instead of hot galvanized steel, pretreated with "Bonder 1303" Alu-zinc coated steel is used. Example 3 The same as Example 1 with the following exception: As third layer is used a polyester 'top coat (DJ216, Coilon polyester from Becker Industrifarg, Sweden) instead of EJ644. SUBSTITUTE SHEET

Claims: CLAIMS 1. A continuous process for surface coating a generally planar metal surface of a sheet or coil in a coil coating line, com¬ prising the steps of: applying as a first layer a paint material with adhesive properties and drying said first layer; applying directly upon the hot paint surface of the first layer a clear, chlorine-free plastic sheet or foil and cooling; applying as a third layer on the cool plastic sheet or foil a pigmented, chlorine-free paint and curing. 2. A process according to Claim 1, c h a r a c t e r i z e d in that the chlorine- free plastic sheet or foil is an acrylic plastic. 3. A process according to Claim 1, c h a r a c t e r i z e d in that the chlorine- free plastic sheet or foil is a poly¬ ester . 4. A process according to any of Claims 1-3, c h a r a c - t e r i z e d in that the chlorine- free paint used as the first layer is a latex paint. 5. A process according to any of Claims 1-3, c h a r a c - t e r i z e d in that the chlorine- free paint in the third layer is a polyester. 6. A process accoring to any of the preceding claims, c h a r a c t e r i z e d in that the chlorine- free plastic sheet or foil used as the second layer has a thickness of from 10 to 300 μm. 7. A process according to any of the preceding claims, c h a r a c t e r i z e d in that the paint used as the third layer is applied to a thickness of from 10 to 150 μm dry film. SUBSTITUTE SHEET

Inventors: HOLMBERG KARL LAGE, HOLMBERG, KARL, LAGE
Applicants: BECKER IND AB, HOLMBERG KARL LAGE, BECKER INDUSTRIFAERG AB, HOLMBERG, KARL, LAGE
Application year: 1994
Main classification: B05D7
IPC codes: B05D7, B32B15